Residents living on Salinas' Acosta Street escaped unscathed from an explosion and three-alarm fire that rapidly spread from a blue house to an apartment building Tuesday.

On Wednesday, firefighters said they determined the fire was sparked by a water heater that ignited a leaking propane hose. The hose ran from the house to an illegal outdoor shed that had a stove and several bunk beds in it.

When firefighters arrived, no one was home. Fire crews battled black smoke and navigated around live power lines in the street until flames were stifled just after 5 p.m.

Although nearly a dozen adults and children lived in the one-story house and backyard shed, firefighters had a hard time finding any renter Tuesday night. The house is owned by Salvador and Luz Torres and they rent it out to a large family.

Apartment manager Guillermo Gomez said the blue house's residents often worked on cars in the garage.

"They were working on cars day and night. One of the tenants was complaining and thought about calling the police because it was kind of dangerous," Gomez said.

The apartment complex and house were destroyed while 100 firefighters stopped the blaze from spreading to a second apartment complex. Four families lived in the gutted apartment complex and were displaced by the fire.